RESOLVED COMPANIONS OF CEPHEIDS: TESTING THE CANDIDATES WITH X-RAY OBSERVATIONS

Journal Article · Fri Apr 15 04:00:00 EDT 2016 · Astronomical Journal (Online)

DOI:https://doi.org/10.3847/0004-6256/151/4/108· OSTI ID:22519954

Evans, Nancy Remage; Pillitteri, Ignazio; Wolk, Scott; Karovska, Margarita; Tingle, Evan ^[1]; Guinan, Edward; Engle, Scott ^[2]; Bond, Howard E. ^[3]; Schaefer, Gail H. ^[4]

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1. Smithsonian Astrophysical Observatory, MS 4, 60 Garden St., Cambridge, MA 02138 (United States)
2. Department of Astronomy and Astrophysics, Villanova University, 800 Lancaster Ave., Villanova, PA 19085 (United States)
3. Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States)
4. The CHARA Array of Georgia State University, Mount Wilson, California 91023 (United States)

We have made XMM-Newton observations of 14 Galactic Cepheids that have candidate resolved (≥5″) companion stars based on our earlier HST Wide Field Camera 3 (WFC3) imaging survey. Main-sequence stars that are young enough to be physical companions of Cepheids are expected to be strong X-ray producers in contrast to field stars. XMM-Newton exposures were set to detect essentially all companions hotter than spectral type M0 (corresponding to 0.5 M{sub ⊙}). The large majority of our candidate companions were not detected in X-rays, and hence are not confirmed as young companions. One resolved candidate (S Nor #4) was unambiguously detected, but the Cepheid is a member of a populous cluster. For this reason, it is likely that S Nor #4 is a cluster member rather than a gravitationally bound companion. Two further Cepheids (S Mus and R Cru) have X-ray emission that might be produced by either the Cepheid or the candidate resolved companion. A subsequent Chandra observation of S Mus shows that the X-rays are at the location of the Cepheid/spectroscopic binary. R Cru and also V659 Cen (also X-ray bright) have possible companions closer than 5″ (the limit for this study) which are the likely sources of X-rays. One final X-ray detection (V473 Lyr) has no known optical companion, so the prime suspect is the Cepheid itself. It is a unique Cepheid with a variable amplitude. The 14 stars that we observed with XMM constitute 36% of the 39 Cepheids found to have candidate companions in our HST/WFC3 optical survey. No young probable binary companions were found with separations of ≥5″ or 4000 au.

• OSTI ID: 22519954
• Journal Information: Astronomical Journal (Online), Journal Name: Astronomical Journal (Online) Journal Issue: 4 Vol. 151; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BINARY STARS
CAMERAS
CEPHEIDS
COSMIC PHOTONS
COSMIC X-RAY SOURCES
MAIN SEQUENCE STARS
STAR CLUSTERS
X-RAY DETECTION